This invention relates to a composite sheet suitable as an important component of disposable garments such as disposable diapers, sanitary napkins and disposable gowns used in medical field and also to a process for making such a composite sheet.
It is well known to use a plastic film or nonwoven fabric as breathable but liquid-resistant sheet constituting disposable garments. As it is well known, a hydrophobic plastic film may be added with grains of inorganic filler such as barium sulfate and then stretched to obtain a liquid-resistant plastic film having fine pores for breathability. As it is also well known, hydrophobic thermoplastic synthetic fiber may be processed to form a nonwoven fabric having an appropriately high fiber density, i.e., appropriately small fiber interstices and thereby presenting desired breathability and liquid-resistance. It is also possible to improve the liquid-resistance by subjecting the nonwoven fabric to water repellent finish.
The term xe2x80x9cliquid-resistancexe2x80x9d used herein should be understood to mean a property enabling permeation as well as exudation of body fluids to be practically avoided.
The plastic film of prior art may give a wearer of the disposable garment using such plastic film so-called plastic-like touch peculiar to such plastic film and the plastic-like touch is often disliked by the wearer. On the contrary, the nonwoven fabric rarely gives the wearer a plastic-like touch even when the nonwoven fabric is made of raw material similar to that of the plastic film. Increasing of the fiber density certainly results in an improvement of the liquid-resistance but at the cost of a soft touch desired for the nonwoven fabric, an increased amount of the fiber used to make the nonwoven fabric and a correspondingly higher cost of the nonwoven fabric.
It is an object of this invention to provide a breathable but liquid-resistant composite sheet offering soft and comfortable touch.
According to a first aspect of this invention, there is provided a composite plastic sheet suitable as an important component of disposable garment and, according to second-fourth aspects of this invention, there is provided a process for making the composite sheet.
The first aspect of this invention relates to an improvement in a composite plastic sheet comprising a first plastic film layer forming an upper surface of the sheet, a second plastic film layer forming a lower surface of the sheet and a thermoplastic synthetic fibrous assembly layer disposed between the first and second plastic film layers and joined to the first and second plastic film layers, respectively.
The improvement according to the first aspect of this invention is in that the first and second plastic film layers and the fibrous assembly layer are hydrophobic; the first plastic film layer includes a plurality of first plane regions spaced one from another and extending parallel one to another in one direction and the second plastic film layer includes a plurality of second plane regions spaced one from another and extending parallel one to another in the one direction wherein each of the first and second plane regions has a thickness of 0.001-0.05 mm and a width of 0.03-1 mm and wherein, of each pair of adjacent the first plane regions and each pair of adjacent the second plane regions, at least each pair of adjacent the first plane regions are connected with each other by a plurality of bridge-like regions extending across the adjacent plane regions; of the first and second plane regions, at least first plane regions are formed along edges thereof with first rising regions extending upward from an upper surface of the plane regions so as to undulate sawtooth waves in the one direction;
the second plastic film layer partially underlies regions of the fibrous assembly layer defined between each pair of adjacent the first plane regions; and the fibrous assembly layer comprises component fibers joined together by mechanical entanglement, heat-sealing or adhesion joined and is joined to a lower surface of the first plane regions and an upper surface of the second plane regions.
The second aspect of this invention relating to a process for making a composite plastic sheet comprises the steps of;
a. continuously feeding a composite web comprising a hydrophobic plastic film web and a thermoplastic synthetic fibrous assembly web underlying the film web and joined to a lower surface of the film web in one direction;
b. subjecting a lower surface of the continuously fed composite web to high pressure columnar water streams and thereby breaking through the film web the high pressure columnar water streams in the one direction according to traces of the high pressure columnar water streams to form the film web with a plurality of first plane regions extending parallel one to another in the one direction, a plurality of openings extending parallel one to another in the one direction between respective pairs of adjacent the first plane regions, a plurality of first rising regions extending from edges of the first plane regions defining respective the openings substantially in the same direction as the high pressure columnar water streams so as to undulate in the one direction substantially like sawtooth waves, and a plurality of bridge-like regions extending across respective the openings to connect each pair of adjacent the plane regions with each other; and
c. joining a plurality of plastic film strips extending parallel one to another in the one direction to a lower surface of the fibrous assembly so that the plastic film strips at least partially underlie portions of the fibrous assembly web defined by respective the openings.
The third aspect of this invention relating also to a process for making a composite plastic sheet comprises the steps of:
a. continuously feeding composite web comprising a plastic film web and a fibrous assembly web underlying the film web and joined to a lower surface of the film web in one direction;
b. subjecting an upper surface of the continuously fed composite web to high pressure columnar water streams and thereby breaking through the film web by the high pressure columnar water streams in the one direction according to traces of the high pressure columnar water streams;
c. subjecting a lower surface of the composite web, substantially in accordance with the traces of the high pressure columnar water streams, to high pressure columnar water streams to form the film web with a plurality of first plane regions extending parallel one to another in the one direction, a plurality of openings extending parallel one to another in the one direction between respective pairs of adjacent the first plane regions, a plurality of first rising regions extending from edges of the first plane regions defining respective the openings substantially in the same direction as the high pressure columnar water streams so as to undulate in the one direction substantially like sawtooth waves, and a plurality of bridge-like regions extending across respective the openings to connect each pair of adjacent the plane regions with each other; and
d. joining a plurality of plastic film strips extending parallel one to another in the one direction to a lower surface of the fibrous assembly web so that the plastic film strips at least partially underlie portions of the fibrous assembly defined by respective the openings.
The fourth aspect of this invention relating also to a process for making a composite plastic sheet comprises the steps of:
a. continuously feeding composite web in one direction, the composite web comprising an upper plastic film web, a lower plastic film web and a fibrous assembly web disposed between the upper plastic film web and joined to a lower surface of the upper plastic film web and to an upper surface of the lower plastic film web in one direction; and
b. subjecting an upper surface of the continuously fed composite web to high pressure columnar water streams and thereby breaking through the upper and lower plastic film web in according with traces of the high pressure columnar water streams in the one direction to form the upper and lower plastic film with a plurality of first plane regions extending parallel one to another in the one direction, a plurality of openings extending parallel one to another in the one direction between respective pairs of adjacent the first plane regions, a plurality of first rising regions extending from edges of the first plane regions defining respective the openings substantially in the same direction as the high pressure columnar water streams so as to undulate in the one direction substantially like sawtooth waves, and a plurality of bridge-like regions extending across respective the openings to connect each pair of adjacent the plane regions with each other.